Portable electronic devices, such as digital cameras for example, generally depend on a battery-based power supply for their operational power. In particular, a battery-based power supply that employs a user-replaceable battery is often used in such portable battery-powered devices. The battery may be either a non-rechargeable battery or a rechargeable battery. In either case, the battery of the battery-based power supply provides the device with operational power without requiring a continuous connection to a fixed power source, such as an alternating current (AC) electrical outlet, thus facilitating portable operation. Typically, the device can be operated from battery power until the battery becomes depleted. When depleted, the battery is either replaced with a fully charged, replacement or the battery is recharged if a rechargeable battery is being used.
Recent advancements in the area of fuel cells have sparked an interest in the use of fuel cells in place of batteries for powering portable electronic devices. Fuel cells, like batteries, directly convert chemical energy of a ‘fuel’ directly into electrical energy that may subsequently be utilized to power a portable device. However, unlike a battery in which the ‘fuel’ is in the form of electrodes in contact with an electrolyte that are more or less permanently enclosed inside the battery, the fuel cell utilizes a replenishable fuel supply to produce electrical energy from chemical energy.
In particular, the advent of so-called ‘micro-fuel cells’ has made it practical to use fuel cells in portable devices. Micro-fuel cells can be made lighter than conventional batteries. Furthermore, effective energy densities of between 1200 to 3000 W-hr per kg (20% to 50% efficiency) have been reported for fuel cells. Such energy densities give fuel cells around 2 to 5 times advantage over a typical energy density of 600 W-hr per kg for rechargeable lithium ion batteries. For example, Hockaday, U.S. Pat. No. 6,326,097 B1 discloses a micro-fuel cell for powering portable devices.
In most cases, a device is equipped with and powered exclusively by either a micro-fuel cell or a battery. In a device exclusively powered by a fuel cell, a user of the device is highly dependent upon being able to obtain a replacement fuel cartridge when the device depletes a currently installed cartridge. On the other hand, a user of a device powered exclusively by a battery is dependent on either obtaining a replacement battery or suspending portable device operations while recharging a rechargeable battery when the battery becomes depleted.
Accordingly, it would be advantageous to have a portable electronic device that could be interchangeably powered using either a battery or a fuel cell, as opposed to using either one exclusively or both jointly. Furthermore, it would be desirable if a user of such a device could readily switch between using the battery and using the fuel cell. Such interchangeable battery and fuel cell power sources would solve a long-standing need in the area of powering portable electronic devices.